The term "polyphenylene ethers" includes a family of polymers well known to those skilled in the art, and they are made by a variety of catalytic and noncatalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes using metal-amine catalysts are found in Bussink et al., U.S. Pat. No. 3,337,499, Blenchard et al., U.S. Pat. No. 3,219,626; Laakso et al., U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,116; Hori et al., U.S. Pat. No. 3,384,619; Faurote et al., U.S. Pat. No. 3,440,217; and processes relating to metal based catalysts which do not include amines, are known from disclosures such as Wieden et al., U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al., U.S. Pat. No. 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al., U.S. Pat. No. 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as a peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al., U.S. Pat. No. 3,382,212. All of the above-mentioned disclosures are incorporated herein by reference.
The term "resinous compositions" in its broadest sense includes various copolymers and blends of the polyphenylene ethers formed by interpolymerization with other monomers or polymers, such as the polyolefins, polystyrenes, polycarbonates and the like, wherein the polyphenylene ether component is present in an amount of, for example, from 1 to 99 parts by weight per 100 parts by weight of the total resinous components of the composition.
The compositions including a polyphenylene ether component can be chemically and physically combined and they can be in liquid media in the form of emulsions, solutions, suspension solution combinations, e.g., as disclosed in U. K. Patent No. 1,291,609, and the like.
Among the most important of such resinous compositions are blends of polyphenylene ethers with styrene resins, including rubber modified polystyrene resins, and graft copolymers of polyphenylene ether resins with styrene resin, including styrene homopolymer resins, and the like. These are described, for example, in Cizek, U.S. Pat. No. 3,383,435, which is incorporated herein by reference. Compositions of polyphenylene ether and polystyrene and of rubber modified polystyrene can also be prepared by the oxidation of the corresponding phenol, e.g., 2,6-dimethyl phenol, in a solution of polystyrene or of polystyrene and a rubber, see, for example, Katchman, U.S. Pat. No. 3,663,661, the disclosure of which is incorporated herein by reference. Reaction mixtures containing graft copolymers of polyphenylene ether resins and styrene resins can also be made by polymerization of vinyl aromatic monomers in the presence of polyphenylene ethers for example, according to the disclosure in Fox, Canadian Patent No. 785,834, which is incorporated herein by reference. A typical process disclosed in Fox involves blending equal parts of poly-2,6-dimethyl-1,4-phenylene oxide and styrene monomer and reacting the blend in the presence of about 1% by weight dicumyl peroxide, based on the styrene monomer.
In general, all of the above processes produce the polyphenylene ether or resinous composition as a component in a liquid medium and a common subsequent step is to add a polymer non-solvent to the liquid medium to precipitate the polymer. For example, if the resinous composition is contained in a medium which includes benzene, toluene, xylene or the like, adding methanol will precipitate the polyphenylene ether. If the resinous composition is contained in pyridine, adding water will precipitate the composition.
Such procedures have disadvantages, including a high energy cost, the need to use complex equipment, a loss in yield due to the number of handling steps required, loss of economy through solvent and non-solvent evaporation and intermingling; and difficulty in controlling particle size distribution in the product.
It has now been discovered that the resinous composition consisting of or including a polyphenylene ether can be conveniently isolated directly from a liquid medium, if one of the liquid components vaporizes readily, by atomizing the resinous composition and liquid medium and removing the liquid component which vaporizes readily from the atomized droplets by contact with a hot inert gas or a superheated, vaporized form of the component which volatilizes readily. The polyphenylene ether, or compositions containing it, is then collected in the form of discrete, fine particles. The process is especially important in its application to polyphenylene ether reaction mixtures, after removal of the metal catalysts and treatment to remove colored impurities, if desired. Benzene and toluene are particularly suitable as the liquid component which vaporizes readily, but others, such as xylene, trichloroethylene and the like may be used.
The novel process has the following advantages over those described in the prior art: (i) lower energy cost; (ii) simpler equipment; and (iii) higher yields.